Resolution of tar bases



, 3-picoline.

Patented Nov. 29, 1949 UNITED STATES PATENT OFFICE RESOLUTION OF TAR BASES Benjamin F. Herr, Jr., Philadelphia, Pa., assignor to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York No Drawing. Application December 22, 1945,

Serial No. 637,080

8 Claims. 1

This invention relates to separation of S-picoline from closely-related heterocyclic nitrogen compounds.

The picolines, other homologs of pyridine, and

' pyrrole are customarily extracted, along with be obtained in reasonably pure form by fractional distillation, but for the most part the remaining compounds cannot be separated by distillation methods alone. Instead, the fractions obtained, even when they are of relatively narrow boiling range, contain increasing numbers of pyridine homologs and their isomers. Mixtures of this kind have found but limited practical application, mainly as special solvents, and are of relatively low economic value. I such as 3-picoline, however, if it could be readily isolated, would be of far greater value, for ex- An individual compound ample, in the preparation of derivatives, especially pharmaceutical products and dyes; thus nicotinic acid, a member of the vitamin B complex, may be readily obtained by oxidation of The requirements for raw material purity in these fields, however, are often quite rigid.

The potentially valuable 3-picoline is found in coal tar nitrogen compound fractions boiling within the range of about 140 to 148 C. But when mixtures of heterocyclic nitrogen compounds are recovered from most types of coal tar,

- lutidine, boiling point 143.8 C., 3-picoline (beta- ,picoline), boiling point l43.9 C., and 4-plcoline (gamma-picoline), boiling point 144.8 C. Mixtures of heterocyclic nitrogen compounds re- ;covered from some of the less common coal tars -may contain substantial proportions of pyrrole instead of, or in addition to, the 2,6-lutidine, since, although pyrrole alone boils at 129.8 C., with 3- and 4-picolines it forms high boiling azeo- .tropes boiling about 145 to 148 0., the components of which are inseparable by ordinary distillation methods.

Since the three components making up the usual nitrogen base fractions in which 3-picoline is found (2,6-lutidine, 3-picoline, and 4-picoline) have substantially the same boiling points, and since pyrrole, presentin some of these fractions, forms azeotropes with these bases, ordinary fractional distillation is obviously unsatisfactory as a means for separating the 3-picoline from such mixtures. Other methods of separating 3-picoline heretofore described in the published prior art have been generally unsatisfactory in regard to products, yields, and production costs.

An object of this invention is to provide a process whereby 3-picoline of a high degree of purity may be recovered from mixtures thereof with like-boiling nitrogen compounds.

I have discovered that high yields of the commercially valuable 3-picoline may be recovered in substantially pure form from mixtures of this base with like-boiling closely-related heterocyclic nitrogen bases such as 4-picoline and 2,6-lutidine, by treating such mixtures with copper sulfate, whereupon a complex addition'compound of copper sulfate and 3-picoline is precipitated to the substantial exclusion of other nitrogen base complexes. The precipitated material is separated from the liquid phase material and the S-picoline may then readily be liberated from the copper sulfate addition compound thereof.

The 3-picoline mixtures that may advantageously be treated by the process of my invention include the various nitrogen base fractions containing B-picoline and like-boiling closelyrelated heterocyclic nitrogen bases such as 4-picoline and 2,6-lutidine. I find it advantageous to treat fractions containing from 15% to by weight of 3-picoline, the remainder of the mixture consisting essentially of one or both of the bases 4-picoline and 2,6-lutidine, and sometimes pyrrole as well.

In all such mixtures, when treated with copper sulfate in accordance with the process of my invention, the 3-picoline reacts preferentially with the copper sulfate to precipitate a complex addition compound, the formula of which is believed to be 2(3-picoline).CuSO4. In the usual commercial 3-picoline fractions as above described. generally boiling within the range of to 148 C. and generally consisting roughly of about one-third 3-picoline, up to 65% of the 3-picoline may be precipitated in the form of its copper sulfate addition compound and, upon separation of the precipitated material and treatment to 'recover 3-picoline therefrom, a 3-picoline prodobtained. A 3-picoline product of such purity is entirely suitable as a starting material for the various products such as pharmaceuticals, etc. for which 3-picoline is in great demand.

In a preferred method of carrying out the proc ess of my invention, a 3-picoline fraction of the type above described is mixed with an aqueous copper sulfate solution. The use of from 1 to 3 mols of copper sulfate per mol of 3-picoline in the mixture being treated has been found advantageous but satisfactory results are obtained employing larger or smaller amounts of copper sulfate; about 1.5 mols of c pper sulfate per mol of 3-picoline is preferred. The aqueous solution of copper sulfate may be of any practicable concentration, e. g. from 50% to 60% copper sulfate by weight. I have found it convenient to warm the mixture somewhat to decrease liquid viscosity and bring aboutmore rapid and complete mixing of the reactants.

When mixing is complete, the reaction mixture is cooled to approximately room temperature or below and filtered, e. g. by centrifuging. In order to obtain the highest purity of 3-picoline, particularly when a substantial concentration of 2,6-

' lutidine was present in the initial mixture treated,

it is desirable to reslurry the filter cake once with water and refilter.

The solid 3-picoline-copper sulfate addition product may then be decomposed by any suitable means; for example the addition of alkali converts the copper sulfate to copper oxide and releases 7 the 3-picoline. The 3-picoline thus released may pound involve passing dry ammonia through the *slurry of the addition compound and steam distilling off the liberated 3-picoline; or adding ammonium hydroxide, containing, for example, 28% ammonia to the slurry, and recovering the oil which separates and washing the liberated oil.

After liberation and separation of the 3-pico- 3 line, the copper ma be recovered from the residue and reconverted to copper sulfate for reuse in the process; For example, when the 3-picoline 'has been liberated by causticization, the copper oxide formed in the process may be separated by filtration and washed to remove sodium sulfate also formed in the causticization step. The copper oxide isthen reacted with sulfuric acid to form cop-per sulfate.

The following examples are illustrative of the process of my invention:

Example 1 A S-pico-line fraction of coal tar bases boiling in the range 140 to 145 C. and containing about 38.7% S-picoline, 37.0% i-picoline, 22.1% 26- lutidine was employed in this run. Copper sulfate (CuSOL5-H2O) was dissolved in an equal weight of water, warmed to about 70 C., and added slowly to the tar base mixture which had been similarly warmed, until about 1.5 mols of copper sulfate had been added for each mol of 3-picoline-present. After the addition was complete and the reactants thoroughly mixed the mixture was- -cooled to C. and centrifuged. The filter cake was slurried with an equal weight of hot water, -.cooled and again centrifuged.

The filter cake from the second centrifuging ture.

was sludged with water and 20% aqueous sodium hydroxide solution was added in amount slightly in excess of that required to convert all the copper sulfate to copper oxide. The resulting mixture was subjected to steam distillation and distillate was collected until no more nitrogen base was coming over from the still. Solid sodium chloride was added to the distillate thus obtained to the point of saturation. The supernatant layer of nitrogen base was withdrawn and dried with solid caustic soda. 66% of the 3-picoline present in the original coal tar base fraction Was thus separated and a 3-picoline product of 95.7 purity was obtained.

A mixture of the 4-picoline and 2,6-lutidine originally present in the fraction treated was obtained by causticizing and distilling the mother liquor from precipitation of the copper sulfate addition compound.

Example 2 Following the same procedure as in Example 1 and employing the same coal tar base fraction, the addition of copper sulfate solution was stopped when about 0.82 mol of copper sulfate had been added for each mol of 3-picoline in the base mixture. The copper sulfate addition compound was separated and treated as described in the previous example. In this run 55% of the 3-pico3ine present in the original coal tar base fraction was recovered as a product of 97% purity.

Example 3 Employing the same coal tar base fraction-as in the previous examples and the same procedure, 1.7 mols of copper sulfate were added for each mol of 3-picoline in the nitrogen base mix- In this run 63% of the 3-picoline present in the original base mixture was eventually recovered as a product of 95.8% purity.

Example 4 Employing the same coal tar base fraction as in the previous examples and the same procedure, 2.6 mols of copper sulfate were added for each mol of 3-picoline. In this run 57% of the 3-picoline present in the original base mixture was eventually recovered as a product of 96% purity.

Example 5 chloride with both picolines to form the addition compound ZnCl2.2(piooline). The reaction mixture was cooled, filtered and the filter cake thoroughly washed with water. Substantially all the 2,6-lutidine present in the original base The 2,6-lutidine could be recovered from this filtrate .by causticization and steam distillation as above described in connection with 3-picoline. The picolines were similarly liberated and recovered from the solid zinc chloride addition compound.

The mixture of 3- and l-picolines thus obtained was treated with copper sulfate solution as described in Example 1 above, employing 1.5 mols of copper sulfate for each mol of 3-picoline present in the mixture. The copper sulfate addltion compound was separated and treated as described in Example 1. Over 77% of the 3picoline was thus recovered as a product of approximately 95% purity.

The mother liquor from precipitation of the copper sulfate addition compound was also cau ticized and distilled as above described in connection with 3-picoline. From this distillate a 4-picoline product of 87% purity was obtained.

Example 5 illustrates the step of precipitating ,1,

the CuSO4 addition compound of 3-picoline from its mixtures with 4-picoline only, while the other examples illustrate precipitation of the S-picoline complex from its mixtures with both 4-picoline and 2,6-lutidine.

imilarly precipitated from its mixtures with 2,6-lutidine alone, and from other mixtures of 3-picoline with one or bothof these closely-related pyridine homologs; for example, a 95% 3-picoline product was obtained by the process of Example 1 from a 3-picoline-4-picoline-2,6- lutidine fraction containing pyrrole.

Since certain changes may be made in carrying out the above process Without departing from the scope of the invention, it is intended The 3-picoline complex is treating the base mixture with copper sulfate to 41;

precipitate 3-picoline in the form of its copper sulfate addition compound, separating the addition compound thus precipitated, and treating the separated addition compound to liberate 3-picoline therefrom.

3. In a process for separation, of B-picoline from a heterocyclic nitrogen compound mixture boiling within the range 140 to 148 C., containing from 15% to 85% by weight of B-picoline and a substantial proportion of at least one of the bases 4-picoline and 2,6-lutidine, the steps that comprise treating the base mixture with copper sulfate to precipitate S-picoline in the form of its copper sulfate addition compound, and separating the addition compound thus precipitated.

4. A process for resolving into its components a nitrogen base mixture containing from 15% to 85% by weight of 3-picoline and substantial proportions of the bases 4-picoline and 2,6-lutidine, which comprises treating the base mixture with zinc chloride to form picoline addition compounds of the zinc chloride, separating said addition compounds, liberating the picolines therefrom, treating the picoline mixture thus recovered with copper sulfate to precipitate 3-picoline in the form of its copper sulfate addition compound, separating the addition compound thus recipitated, treating the separated addition compound with a reagent capable of reacting with the copper sulfate 6 to liberate 3-picoline therefrom, and distilling off the liberated 3-picoline.

5. A process for separation of 3-picoline from a mixture thereof with pyrrole and at least one of the bases 4-picoline and 2,6-lutidine, which comprises treating the base mixture with copper sulfate selectively to precipitate 3-pic0line in the form of its copper sulfate addition compound, and separating the addition compound thus precipitated.

6. In a process for separation of 3-picoline from a heterocyclic nitrogen compound mixture boiling within the range 140 C. to 148 0., con taining from 15% to 85% by weight of 3-picoline and a substantial proportion of at least one of the bases 4-picoline and 2,6-lutidine, the steps which comprise adding to the nitrogen base mixture an aqueous solution of copper sulfate containing between about 1 and about 3 mols of copper sulfate per mol of 3-picoline present in the mixture, to precipitate 3=picoline in the form of its copper sulfate addition compound and separating the addition compound thus precipitated.

'7. In a process for separation of B-picoline from a heterocyclic nitrogen compound mixture boiling within the range 140 C. to 148 0., containing from 15% to 85% by weight of 3-picoline and a substantial proportion of at least one of the bases 4-picoline and 2,6-lutidine, the steps which comprise adding to the nitrogen base mixture at a temperature of about C. an aqueous solution of copper sulfate having a copper sulfate concentration between about 50% and about 60% and containing between about 1 and about 3 mols of copper sulfate per mol of 3-picoline present in the mixture, to precipitate 3-picoline in the form of its copper sulfate addition compound, cooling the mixture to a temperature of about 20 C., and separating the precipitated addition compound.

8. In a process for separation of S-picoline from a heterocyclio nitrogen compound mixture boiling within the range 140 C. to 148 C., containing from 15% to by weight of 3-picoline and a substantial proportion of the base 4-picoline and 2,6-lutidine, the steps which comprise adding to the nitrogen base mixture at a temperature of about 70 C. an aqueous solution of copper sul fate having a copper sulfate concentration between about 50% and about 60% and containing between about 1 and about 3 mols of copper sulfate per mol of 3-picoline present in the mixture, to precipitate 3-picoline in the form of its copper sulfate addition compound, cooling the mixture to a temperature of about 20 C., separating the precipitated addition compound by filtration, reslurrying the filter cake with water and refiltering.

BENJAMIN F. HERE, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,035,583 Bailey Mar. 31, 1936 2,259,896 Lake Oct. 21, 1941 2,336,502 Reimers Dec. 14, 1943 

